Flooding or inundation is a widespread problem, whether it occurs in an urban, rural, or wetland setting. In most cases, sea level rise and tidal and nuisance flooding can be predicted and prepared for, but storm surge flooding driven by tropical storms or hurricanes is much more disruptive and less able to predict. By simulating flooding for a wide variety of scenarios, you can identify areas that will be potentially impacted, understand the associated risk, and adapt by building response and resilience plans.
In any flooding scenario, understanding the relationship between predicted flood height (water-level), the local terrain, and the built environment is critical in determining how to prepare for, and respond to, these flood events. GIS provides the environment to simulate these events and identify potential risks. The resulting layers and maps can be used to quantify the risk to infrastructure, critical facilities, and the citizens of the community.
These analyses are critical for developing both response plans and community resilience plans that provide insight to both emergency response teams and community planners to prepare in both the near term and long term, respectively.
Workflows
ArcGIS provides several workflows and tools to analyze and visualize the impacts of flooding events. You can quickly explore the impact of flooding by selecting which assets are affected within a flooded area or you can do a more thorough analysis and calculate the depth of flooding for each asset and visualize the result in 3D.
Explore flood impact
A quick way of exploring which assets are affected by a particular flood event is to use the Select Features by Location geoprocessing tool in ArcGIS Pro. You need a polygon layer that describes the area of the flooding, also known as a flood boundary, for a particular flooding event, and a layer for each of the assets that might be affected.
Flood boundaries for various flooding scenarios can typically be downloaded from national organizations such as FEMA or NOAA or at a regional level from district or city councils.
It's important to note that this workflow will only indicate which assets are affected by the flooding event, providing information on the spatial relationship between the flood boundary and the assets. It does not provide insight into the extent or severity of the flood impact on each asset.
Analyze flood impact
To be able to analyze how much each asset will be potentially flooded, you will need a flood depth raster. A flood depth raster contains a flood depth value within each cell in the raster. They can also be obtained from sources at a national level such as FEMA or NOAA (National Weather Service, National Hurricane Center of the Office of Coast Management) or at a regional level from, for example, engineering firms.
Examples of flood depth data:
You can use these flood depth rasters in the Flood Impact Analysis solution to analyze and visualize the impacts of flooding events. It provides a guided, task-based workflow for analyzing common flooding events, such as NOAA Sea Level Rise, FEMA Flooding, Tidal Flood, Storm Surge, or custom flooding scenarios. Combining a flood depth raster with a digital terrain model, flood impacts can be calculated for critical infrastructure features such as buildings, roads, low water crossings, or bridges.
Flooding analysis not only allows understanding of areas that are directly impacted, but it also helps identify areas that are cut-off or inaccessible due to flooding. Identifying these secondary impacts can be extremely useful for emergency response and critical facility allocation and placement.
Visualize flood impact in 3D
The Flood Impact Analysis solution can also be used to create compelling 3D visualizations that make it easier to understand and communicate the real impact of the flooding scenarios. You can drape the results from the analysis on the terrain or integrated mesh and thematically symbolize the features in the scene. 3D features such as buildings can also be used as input for the flood impact analysis.
It is also possible to show the water level in 3D to get a visual indication of how much an asset is going to be flooded.
Considerations
Data quality plays a crucial role in carrying out a flood impact analysis as it directly affects the accuracy, reliability, and usefulness of the results. Ensure you work with flood data that has associated metadata that describes how it was calculated.
After you have done the flood impact analysis, you can further improve the user experience by bringing the results into a web app, mobile app, or game engine. This allows you to not only visualize the impact of flooding but also show indicators highlighting the impact on each asset layer for each flooding scenario.
Required software
You'll need ArcGIS Pro to explore the impact of flooding. The 3D Analyst extension is required to use the Flood Impact Analysis solution. You will need anArcGIS Online or ArcGIS Enterprise account to publish and share the results across your organization.
Explore the following resources to learn more about analyzing flood impact in ArcGIS.
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